1. Field of the Invention
The present invention relates to a light-emitting device, preferably having a Group III nitride compound semiconductor light-emitting element mounted.
2. Description of the Related Art
As a related-art light-emitting element based on attention directed to the transparency of a substrate used for a Group III nitride compound semiconductor, there is known a flip chip (hereinafter also abbreviated to “FC”) type light-emitting element having a substrate surface on its upper side so that the substrate surface serves as a light-emitting surface. The light-extracting efficiency of the flip chip type light-emitting element is higher than that of a light-emitting element of the type of extracting light from the electrode side (hereinafter also referred to as “FU”).
As shown in FIG. 1, interposition of a sub-mount 5 is however essential for mounting the flip chip type light-emitting element 1 on a mount frame 3. A special mount device is further required for mounting the light-emitting element 1 so that the substrate of the light-emitting element 1 turns upward. It is further necessary to deepen a concave portion 4 of the mount frame 3 by at least the height of the sub-mount 5 so that light emitted from the light-emitting element 1 to a side can be reflected toward the optical axis so as to be utilized effectively. This causes increase in production cost of the mount frame 3 and, accordingly, increase in production cost of the light-emitting device.
There has been proposed a light-emitting device in which a downward facing substrate surface of a flip chip type light-emitting element is fixed to a surface of a light-transmissive member with which a concave portion of a mount frame is filled (Related Art 1).
There has been proposed a light-emitting device having a light-emitting element of the type of extracting light from the electrode side, in which a reflecting block is protruded from a bottom surface of a mount frame (Related Art 2).
In the light-emitting device according to Related Art 1, the light-emitting element having a substrate surface as a main light-emitting surface can be mounted without use of any sub-mount. Accordingly, an inexpensive light-emitting device can be provided while the light-emitting efficiency of the light-emitting element is kept high. According to the inventors' examination, however, the following problem to be solved has been found.
That is, it is difficult to give the light-transmissive member heat conductivity sufficient to release heat caused by light emission. As a result, when a high-output light-emitting element is mounted, there is a possibility that the life of the light-emitting element may be shortened because of insufficient heat radiation.
It is also difficult to give the light-transmissive member sufficient mechanical stiffness. Accordingly, there is fear in the mount stability of the light-emitting element. When, for example, wire bonding is performed by high-frequency heating after the light-emitting element is fixed to the light-transmissive member, there is a possibility that vibration may be absorbed to the light-transmissive member to make the wire bonding impossible. Accordingly, there is a possibility that the quality of the light-emitting device may vary.
In the light-emitting device according to Related Art 2, a light-emitting element having a main light-emitting surface on the electrode surface side is used. This type light-emitting element is structurally inferior in light-emitting output to a light-emitting element having a main light-emitting surface on the substrate surface side. One of reasons is light shielding of a bonding electrode and low light transmittance of a light-transmissive electrode. When a light-transmissive thin-film electrode as used in the light-emitting device according to Related Art 2 is used, deterioration (ball-up) of the thin-film electrode per se or deterioration (ball-up) of the thin-film electrode at a junction surface between the thin-film electrode and a seat electrode occurs as the amount of heat generated in the light-emitting element increases.
As described above, the light-emitting device according to Related Art 2 includes the problem (in difficulty in obtaining a high output from the light-emitting element, and low light-extracting efficiency) which has been already solved in Related Art 1.